At this time of year, probably just mice! But there are birds, like chickadees (similar to your long-tailed tits) that pile into cavities en masse to conserve warmth out of the wind. They can lose 25% of their weight overnight when it is bitterly cold.

This is my diary of the wildlife where I live in Oxfordshire, and sometimes the places I visit. I am a 15 year old young naturalist with a passion for British wildlife, especially Badgers and Hares. I have been blogging since May 2013 and you can read my old blog posts at www.appletonwildlifediary.blogspot.co.uk